A multi-channel voltage detector as shown in FIG. 5 has been proposed in the art. The apparatus includes terminals 51-1 through 51-n to which multi-channel electrical signals are applied, a plurality of converters for converting the multi-channel electrical signals into the corresponding optical signals, and a streak camera 55 to which output optical signals of converters 52-1 through 52-n are applied through optical fibers 54-1 through 54-n, respectively.
In this apparatus, electrical signals applied to the terminals 51-1 through 51-n modulate laser diodes 53-1 through 53-n, respectively, in the respective converters 52-1 through 52-n. The variations in intensity of the optical signals outputted by the laser diodes 53-1 and 53-n are simultaneously observed with one streak camera 55 to detect the multi-channel electrical signals in a parallel mode.
In the above-described multi-channel voltage detector, the modulation-permitted frequency of the laser diodes 53-1 through 53-n in the converters 52-1 through 52-n is of the order of a maximum of 1 GHz, and the time resolution is of the order of 350 picoseconds. Therefore, the apparatus suffers from a difficulty that it cannot detect higher frequency electrical signals with high time resolution.